1. Field of the Invention
This invention relates to a ball joint for a stabilizer, which couples a wheel axle of a vehicle to a torsion bar and, more particularly, to a pillow ball seat for swingably supporting a stud ball.
2. Description of the Prior Art
With vehicles being driven at increasingly high speeds, there is a need for providing vehicles with greater stability. Specifically, it is necessary to ensure against vehicle tip-over during sharp cornering. Accordingly, many recent vehicles adopt a system in which each wheel axle is coupled to a torsion bar in order to minimize the level difference between the left and right wheels. As a member for coupling the torsion bar and wheel axle, a pair of ball joints having three-dimensional coupling means are used.
FIGS. 3 and 4 show prior art ball joints for a stabilizer, in which a stud ball 1 made of metal has a spherical head 2 fitted in a ball seat member 3 made of synthetic resin by making use of the elasticity of the member 3 so that an equator portion 4 of the spherical head 2 is swingably supported on an annular concave spherical surface 5 formed in the inner periphery of the ball seat member 3.
For the purpose of preventing the fitted spherical head 2 of the stud ball 1 from being detached from the inner periphery of the ball seat member 3 and coupling together a pair of ball joints with a connecting rod 6, in the prior art shown in FIG. 3, the ball seat member 3 is inserted downwardly into an outer cylindrical member 8 made of steel and having an inner projection 7 projecting from the lower end of the inner periphery. The lower end of the ball seat member 3 is thus supported on the inner projection 7. Then, a circular lid 9 made from steel plate material is fitted in the outer cylindrical member 8 such that its edge is supported on the top of the ball seat member 3. Thereafter, an upper portion 8' of the outer cylindrical member 8 is calked inwardly against the edge of the circular lid 9.
In the prior art ball joint shown in FIG. 4, an outer blind cylindrical member 12 made of steel and having a top wall 10 and an inner shoulder portion 11 in contact with the top of the ball seat member 3 is fitted downwardly on the ball seat member 3 so that the inner shoulder portion 11 is supported on the top of the ball seat member 3. Then, a lower end portion 12' of the outer cylindrical member 12 is calked inwardly against the lower surface of the ball seat member 3.
However, with the ball joint shown in FIG. 3, it is necessary to provide the outer cylindrical member 8 with the inner projection 7 by cold forging from steel. This operation requires a large number of steps and leads to high cost. Likewise, with the ball joint shown in FIG. 4 it is necessary to provide the outer cylindrical member 12 with the inner shoulder 11 and top wall 10 by cold forging from steel. Again this operation requires a large number of steps and leads to high cost.
Further, the assembling operation requires a calking step of inwardly bending and calking the upper end portion of the outer cylindrical member 8 in the case of the ball joint of FIG. 3 and the lower end portion of the outer cylindrical member 12 in the case of the ball joint of FIG. 4, and this leads to increased cost.
Further, with the ball joint shown in FIG. 4 in which the lower end portion of the outer cylindrical member 12 is inwardly calked, it is difficult to mount a flexible boot for keeping out dust. More specifically, the boot cannot be reliably mounted by using a groove and is therefore inevitably bonded by adhesive to the outer cylindrical member 11.
An object of the invention is to provide a pillow ball seat of a ball joint for a stabilizer, which can be manufactured readily and at low cost.